1. Field of the Invention
The invention relates to a circuit board structure and the fabricating method thereof, more specifically, the invention relates to a circuit board structure with concave conductive cylinders and the fabricating method thereof.
2. Description of Related Art
Generally, conventional circuit boards used to carry and electrically connect a plurality of electronic elements are mainly formed with a plurality of interlayered patterned conductive layers and dielectric layers. The patterned conductive layers are defined and formed through patterning copper foil directly, or through copper electroplating upon copper foil to increase the thickness of conductive layer and then go through a patterning process. The dielectric layers are respectively disposed between these adjacent patterned conductive layers to insulate these patterned conductive layers. In addition, the interlayered patterned conductive layers are electrically connected to each other through conductive vias. In addition, various electronic elements (e.g. active elements or passive elements) may be further disposed on a surface of the circuit board, and through the internal circuit in the circuit board to realize electrical signal propagation.
FIG. 1 is a section view of a circuit board of prior arts. With reference to FIG. 1, a patterned conductive layer 120 of a circuit board 100 of prior arts is disposed on a dielectric layer 110, and the patterned conductive layer 120 has a plurality of pads 122. A patterned solder mask layer 130 is disposed on the dielectric layer 110 to cover a portion of the patterned conductive layer 120. The patterned solder mask layer 130 has a plurality of openings 132 to expose these pads 122. In addition, a plurality of solder balls 140 are respectively disposed on these pads 122 and are respectively electrically connected to these pads 122.
However, during the fabricating process of the circuit board 100 of prior arts, when the patterned solder mask layer 130 is formed, the locations of the openings 132 may not be accurately aligned to the pads 122, and drifts may occur accordingly. And therefore a portion of the pads 122 (with reference to the pads 122 on the right side of FIG. 1) are covered too much by the patterned solder mask layer 130. In addition, when an image transfers, light leaking, under exposure, less developing power or incomplete development may also lead to too small openings 132. Therefore, when the solder balls 140 are respectively formed on the pads 122, the contact area between a portion of the solder balls 140 (with reference to the solder balls on the right side of FIG. 1) and the corresponding pads 122 become small, therefore the bonding reliability between a portion of the solder balls 140 and the corresponding pads 122 is reduced.